Multi-phase filter medium

ABSTRACT

Multi-phase filter media, as well as related articles, components, filter elements, and methods, are disclosed.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/012,711, filed Aug. 28, 2013, which is a continuation of U.S.application Ser. No. 13/304,678 (now U.S. Pat. No. 8,545,587), filedNov. 27, 2011, which is a divisional of U.S. application Ser. No.12/488,033 (now U.S. Pat. No. 8,357,220), filed Jun. 19, 2009, whichclaims priority to U.S. Provisional Application No. 61/112,617 filedNov. 11, 2008, which are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

This disclosure relates to multi-phase filter media, as well as relatedarticles, components, filter elements, and methods.

BACKGROUND

Filter media are used in a variety of systems. The media are typicallyused to remove undesirable materials (e.g., particles) from a liquid orgas by passing the liquid or gas through the media.

SUMMARY

In one aspect, this disclosure features an article that includes firstand second phases. The first phase includes a first plurality of fibersand a second plurality of fibers different from the first plurality offibers. The second phase includes a third plurality of fibers and afourth plurality of fibers different from the third plurality of fibers.The third plurality of fibers are the same as or different from thefirst or second plurality of fibers. The fourth plurality of fibers arethe same as or different from the first or second plurality of fibers.The air permeability of the first plurality of fibers is higher than theair permeability of the second plurality of fibers. The air permeabilityof the third plurality of fibers is higher than the air permeability ofthe fourth plurality of fibers. The air permeability of the fibers isdefined in the Detailed Description section below. At least one of thefirst, second, third, and fourth pluralities of fibers are made from anorganic polymeric material. The basis weight ratio of the first phase tothe second phase is from about 30:70 to about 70:30. The article isconfigured as a filter medium.

In another aspect, this disclosure features an article that includesfirst and second phases. The first phase includes a first plurality offibers and a second plurality of fibers different from the firstplurality of fibers. The second phase includes a third plurality offibers and a fourth plurality of fibers different from the thirdplurality of fibers. The third plurality of fibers are the same as ordifferent from the first or second plurality of fibers. The fourthplurality of fibers are the same as or different from the first orsecond plurality of fibers. The pressure drop of the first plurality offibers is lower than the pressure drop of the second plurality offibers. The pressure drop of the third plurality of fibers is lower thanthe pressure drop of the fourth plurality of fibers. The pressure dropof the fibers is defined in the Detailed Description section below. Atleast one of the first, second, third, and fourth pluralities of fibersare made from an organic polymeric material. The basis weight ratio ofthe first phase to the second phase is from about 30:70 to about 70:30.The article is configured as a filter medium.

In another aspect, this disclosure features an article that includesfirst and second phases. The first phase includes a first plurality ofsoftwood fibers. The second phase includes a first plurality of hardwoodfibers. The basis weight ratio of the first phase to the second phase isfrom about 30:70 to about 70:30. The article is configured as a filtermedium.

In another aspect, this disclosure features an article that includesfirst and second phases. The first phase includes first and secondpluralities of fibers. The first plurality of fibers are prepared from amaterial (e.g., softwood fibers) different from a material (e.g.,hardwood fibers or a different type of softwood fibers) used to preparethe second plurality of fibers. The second phase includes third andfourth pluralities of fibers. The third plurality of fibers are preparedfrom a material (e.g., softwood fibers) different from a material (e.g.,hardwood fibers or a different type of softwood fibers) used to preparethe fourth plurality of fibers. The third plurality of fibers are thesame as or different from the first or second plurality of fibers. Thefourth plurality of fibers are the same as or different from the firstor second plurality of fibers. The air permeability of the firstplurality of fibers is higher than the air permeability of the secondplurality of fibers. The air permeability of the third plurality offibers is higher than the air permeability of the fourth plurality offibers. The basis weight ratio of the first phase to the second phase isfrom about 30:70 to about 70:30. The article is configured as a filtermedium.

In still another aspect, this disclosure features an article thatincludes first and second phases. The first phase includes first andsecond pluralities of fibers. The first plurality of fibers are preparedfrom a material (e.g., softwood fibers) different from a material (e.g.,hardwood fibers or a different type of softwood fibers) used to preparethe second plurality of fibers. The second phase includes third andfourth pluralities of fibers. The third plurality of fibers are preparedfrom a material (e.g., softwood fibers) different from a material (e.g.,hardwood fibers or a different type of softwood fibers) used to preparethe fourth plurality of fibers. The third plurality of fibers are thesame as or different from the first or second plurality of fibers. Thefourth plurality of fibers are the same as or different from the firstor second plurality of fibers. The pressure drop of the first pluralityof fibers is lower than the pressure drop of the second plurality offibers. The pressure drop of the third plurality of fibers is lower thanthe pressure drop of the fourth plurality of fibers. The basis weightratio of the first phase to the second phase is from about 30:70 toabout 70:30. The article is configured as a filter medium.

In still another aspect, this disclosure features an article thatincludes first and second phases. The first phase includes a firstplurality of fibers and a second plurality of fibers different from thefirst plurality of fibers. The second phase includes a third pluralityof fibers and a fourth plurality of fibers different from the thirdplurality of fibers. The third plurality of fibers are the same as ordifferent from the first or second plurality of fibers. The fourthplurality of fibers are the same as or different from the first orsecond plurality of fibers.

The air permeability of the first plurality of fibers is higher than theair permeability of the second plurality of fibers. The air permeabilityof the third plurality of fibers is higher than the air permeability ofthe fourth plurality of fibers. At least one of the first, second,third, and fourth pluralities of fibers are made from an organicpolymeric material. The first phase has a higher air permeability thanthe second phase. The basis weight ratio of the first phase to thesecond phase is about 30:70 or greater. The article is configured as afilter medium.

In yet another aspect, this disclosure features a filter element thatincludes one of the articles described above.

In a further aspect, this disclosure features a method that includes (1)disposing through a wet laid process a first dispersion containing firstand second pluralities of fibers described above in a first solvent ontoa wire to form a first phase, (2) while the first and second pluralitiesof fibers are on the wire, disposing a second dispersion containingthird and fourth pluralities of fibers described above in a secondsolvent onto the first and second pluralities of fibers to form a secondphase, and (3) at least partially removing the first and secondsolvents, thereby resulting in one of the articles described above.

Embodiments can include one or more of the following features.

The air permeability of the first or third plurality of fibers can befrom about 50 CFM to about 350 CFM (e.g., from about 100 CFM to about200 CFM). The air permeability of the second or fourth plurality offibers can be from about 5 CFM to about 50 CFM (e.g., from about 15 CFMto about 25 CFM).

The weight ratio of the first and second pluralities of fibers can befrom about 50:50 to about 90:10 (e.g., from about 50:50 to about 70:30or from about 60:40 to about 70:30). The weight ratio of the third andfourth pluralities of fibers can be from about 10:90 to about 50:50(e.g., from about 25:75 to about 50:50 or from about 30:70 to about50:50).

The pressure drop of the first or third plurality of fibers can be fromabout 5 Pa to about 300 Pa (e.g., from about 20 Pa to about 100 Pa). Thepressure drop of the second or fourth plurality of fibers can be fromabout 300 Pa to about 1,000 Pa (e.g., from about 250 Pa to about 500Pa).

The first or third plurality of fibers can have an average fiber lengthfrom about 1.5 mm to about 6 mm. The second or fourth plurality offibers can have an average fiber length from about 0.5 mm to about 2 mm.

The first or third plurality of fibers can include softwood fibers(e.g., fibers obtained from mercerized southern pine, northern bleachedsoftwood kraft, southern bleached softwood kraft, or chemically treatedmechanical pulps), cotton fibers, polyester fibers, polyvinyl alcoholbinder fibers, or rayon fibers. The second or fourth plurality of fiberscan include hardwood fibers (e.g., fibers obtained from Eucalyptus),polyethylene fibers, or polypropylene fibers.

The basis weight ratio of the first and second phases can be from about30:70 to about 70:30, from about 40:60 to about 60:40, or from about30:70 to about 90:10. In certain embodiments, the basis weight ratio ofthe first and second phases is about 30:70 or greater (e.g., about 40:60or greater, about 50:50 or greater, or about 60:40 or greater). In somecases, the first phase has a higher air permeability than the secondphase.

The article can further include a binder (e.g., polyvinyl acetate, anepoxy, a polyester, a polyvinyl alcohol, an acrylic such as a styreneacrylic, or a phenolic resin). The binder can be at least about 2% or atmost about 35% of the basis weight of the article.

The article can have an average pore size from about 3 microns to about1,000 microns (e.g., from about 25 microns to about 125 microns).

The article can have a dust holding capacity from about 0.3 g to about 3g (e.g., from about 1 g to about 3 g) measured according to a Palas flatsheet test.

The article can have an initial dust capture efficiency from about 25%to about 99.5% (e.g., from about 60% to about 99.5%).

The first and third pluralities of fibers can be prepared from the samematerial, or the second and fourth pluralities of fibers can be preparedfrom the same material. The first and second pluralities of fibers canbe prepared from the same material, or the third and fourth pluralitiesof fibers can be prepared from the same material.

The first plurality of fibers can be prepared from a material differentfrom a material used to prepare the second plurality of fibers, or thethird plurality of fibers can be prepared from a material different froma material used to prepare the fourth plurality of fibers.

Each of the first, second, third, and fourth pluralities of fibers canbe made from an organic polymeric material.

The first or second phase can include one or more additional pluralitiesof fibers.

The interface between the first and second phases can be substantiallynon-linear or substantially free of an adhesive.

The filter element can include a radial filter element, a panel filterelement, or a channel flow element.

The filter element can include a gas turbine filter element, a dustcollector element, a heavy duty air filter element (e.g., containing afilter medium in which the weight ratio of the first and secondpluralities of fibers is from about 85:15, and the weight ratio of thethird and fourth pluralities of fibers is from about 49:51), anautomotive air filter element (e.g., containing a filter medium in whichthe first phase includes three pluralities of fibers with a weight ratioof about 83:10:7, and the second phase includes three pluralities offibers with a weight ratio of about 40:35:25), a HVAC air filterelement, a HEPA filter element, a vacuum bag filter element, a fuelfilter element, or an oil filter element.

The first phase can further include a second plurality of hardwoodfibers, the second plurality of hardwood fibers being the same as ordifferent from the first plurality of hardwood fibers.

The second phase can further include a second plurality of softwoodfibers, the second plurality of softwood fibers being the same as ordifferent from the first plurality of softwood fibers.

Embodiments can provide one or more of the following advantages.

Without wishing to be bound by theory, it is believed that, by blendingfibers with different characteristics in one or more phases, one canobtain a filter medium having a multi-phase structure (e.g., havingphases with different air permeabilities and/or pressure drops) withsignificantly improved dust holding capacity and/or dust captureefficiency without substantial degradation in mechanical strengthcompared to a filter medium having a single phase structure (e.g.,having a uniform air permeability and/or pressure drop within thestructure).

Other features, objects, and advantages of the invention will beapparent from the description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a filter medium;

FIG. 2 is a cross-sectional view of a pleated filter medium;

FIG. 3 is partial cut-away perspective view of a filter elementincluding a filter medium.

FIG. 4 is a scanning electron microscope graph illustrating across-sectional view of a dual phase filter medium.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

This disclosure relates to multi-phase filter media, as well as relatedarticles, components, filter elements, and methods. FIG. 1 is across-sectional view of an exemplary filter medium 10 that includes afirst phase 12 and a second phase 16. FIG. 2 depicts a typical pleatedconfiguration of filter medium 10. FIG. 3 shows a cut-away perspectiveof an exemplary filter element 100 including a filter housing 101, afilter cartridge 102, an inner screen 108 and an outer screen 103.Filter medium 10 is disposed in filter cartridge 102. During use, a gasor liquid enters element 100 via an opening 104 and then passes throughinner screen 108, filter medium 10 and outer screen 103. The gas orliquid then exits filter element 100 via opening 106. FIG. 4 is ascanning electron microscope graph illustrating a cross-sectional viewof an exemplary filter medium 10.

I. Filter Medium

As shown in FIG. 1, filter medium 10 includes a first phase 12 and asecond phase 16. In some embodiments, first phase 12 has a larger airpermeability and/or a smaller pressure drop than those of second phase16. Such a phase 12 is hereinafter referred to as an open phase, andsuch a phase 16 is hereinafter referred to as a tight phase. The orderof open and tight phases in filter medium 10 is not critical. In someembodiment, first phase 12 can be a tight phase and second phase 16 canbe an open phase.

Without wishing to be bound by theory, it is believed that a filtermedium having a multi-phase structure (e.g., having phases withdifferent air permeabilities and/or pressure drops) exhibitssignificantly improved dust holding capacity and/or dust captureefficiency compared to a filter medium having a single-phase structure(e.g., having a uniform air permeability and/or pressure drop within thestructure).

A. Open Phase

An open phase in filter medium 10 typically includes a first pluralityof fibers and a second plurality of fibers, although in someembodiments, only a first plurality of fibers is used to form the openphase.

In some embodiments, the first plurality of fibers have an airpermeability larger than that of the second plurality of fibers. Forexample, the first plurality of fibers can have an air permeability fromabout 50 cubic feet per minute (“CFM”) to about 350 CFM (e.g., fromabout 100 CFM to about 200 CFM), and the second plurality of fibers canhave an air permeability from about 5 CFM to about 50 CFM (e.g., fromabout 8 CFM to about 37 CFM or from about 15 CFM to about 25 CFM). Asused herein, air permeability of fibers is determined by measuring theair permeability of a hand sheet produced exclusively by such fibers andhaving a basis weight of 100 g/m² according to ISO 9237.

In some embodiments, the first plurality of fibers have a pressure dropsmaller than that of the second plurality of fibers. For example, thefirst plurality of fibers can have a pressure drop from about 5 Pascals(“Pa”) to about 300 Pa (e.g., from about 10 Pa to about 250 Pa or fromabout 20 Pa to about 100 Pa), and the second plurality of fibers canhave a pressure drop from about 300 Pa to about 1,000 Pa (e.g., fromabout 350 Pa to about 500 Pa). As used herein, pressure drop of fibersis determined by using a gas having a face velocity of 40 cm/s on a handsheet produced exclusively by such fibers and having a basis weight of100 g/m² according to ASTM F778-88.

In some embodiments, the first plurality of fibers have an average fiberlength larger than that of the second plurality of fibers. For example,the first plurality of fibers can have an average fiber length fromabout 1.5 mm to about 6 mm (e.g., from about 2.5 mm to about 4.5 mm),and the second plurality of fibers can have an average fiber length fromabout 0.5 mm to about 2 mm (e.g., from about 0.7 mm to about 1.5 mm).

In general, the materials that can be used to form the first and secondpluralities of fibers can vary as desired. In some embodiments, thefirst plurality of fibers are made from softwood fibers, cotton fibers,glass fibers, polyester fibers, polyvinyl alcohol binder fibers, orrayon fibers. Exemplary softwood fibers include fibers obtained frommercerized southern pine (“mercerized southern pine fibers or HPZfibers”), northern bleached softwood kraft (e.g., fibers obtained fromRobur Flash (“Robur Flash fibers”)), southern bleached softwood kraft(e.g., fibers obtained from Brunswick pine (“Brunswick pine fibers”)),or chemically treated mechanical pulps (“CTMP fibers”). For example, HPZfibers can be obtained from Buckeye Technologies, Inc., Memphis, Tenn.;Robur Flash fibers can be obtained from Rottneros AB, Stockholm, Sweden;and Brunswick pine fibers can be obtained from Georgia-Pacific, Atlanta,Ga.

In some embodiments, the second plurality of fibers are made fromhardwood fibers, polyethylene fibers, or polypropylene fibers. Exemplaryhardwood fibers include fibers obtained from Eucalyptus (“Eucalyptusfibers”). Eucalyptus fibers are commercially available from, e.g., (1)Suzano Group, Suzano, Brazil (“Suzano fibers”), (2) Group PortucelSoporcel, Cacia, Portugal (“Cacia fibers”), (3) Tembec, Inc.,Temiscaming, QC, Canada (“Tarascon fibers”), (4) Kartonimex Intercell,Duesseldorf, Germany, (“Acacia fibers”), (5) Mead-Westvaco, Stamford,Conn. (“Westvaco fibers”), and (6) Georgia-Pacific, Atlanta, Ga. (“LeafRiver fibers”). In general, softwood fibers have a relatively large airpermeability, small pressure drop, and large average fiber lengthcompared to hardwood fibers.

In some embodiments, an open phase can include a mixture of softwoodfibers and hardwood fibers. In certain embodiments, the open phase caninclude only one type of fibers (e.g., softwood fibers) uniformlydistributed within the open phase.

In some embodiments, an open phase can include a mixture of fibers withdifferent characteristics (e.g., different air permeabilities and/orpressure drops). Fibers with different characteristics can be made fromone material (e.g., by using different process conditions) or differentmaterials.

In some embodiments, the first plurality of fibers can be formed from amaterial identical to the material used to form the second plurality offibers. In such embodiments, the first and second pluralities of fiberscan be prepared by using different preparation methods, or differentconditions in the same preparation method, such that they have differentcharacteristics (e.g., different air permeabilities or pressure drops).In certain embodiments, the first and second pluralities of fibers canbe formed of the same material and also have the same characteristics.In some embodiments, the first plurality of fibers can be formed from amaterial different from the material used to form the second pluralityof fibers.

Generally, the weight ratio of the first and second plurality of fiberscan vary depending on the desired properties of filter medium 10. Anopen phase in filter medium 10 typically includes fibers with a largerair permeability and/or a smaller pressure drop in an amount larger thanthe amount of fibers with a smaller air permeability and/or a largerpressure drop. For example, a weight ratio of the first and secondpluralities of fibers described above can range from about 50:50 toabout 97:3 (e.g., from about 50:50 to about 70:30 or from about 60:40 toabout 70:30). As used herein, the weight of the first or secondplurality of fibers refers to the initial weight of each group of fibersin a composition (e.g., a pulp) used to prepare the open phase. Incertain embodiments, an open phase in filter medium 10 can includefibers with a larger air permeability and/or a smaller pressure drop inan amount equal to or smaller than the amount of fibers with a smallerair permeability and/or a larger pressure drop.

In some embodiments, an open phase can include one or more pluralitiesof fibers in addition to the first and second pluralities of fibers.Each of the additional pluralities of fibers can have characteristics(e.g., air permeability and/or pressure drop) different from the firstor second plurality of fibers, or can be prepared from a materialdifferent from those used to prepare the first or second plurality offibers. In some embodiments, an additional plurality of fibers can beprepared from a material identical to a material used to form one of thefirst and second pluralities of fibers, but still have characteristicsdifferent from those of the first or second plurality of fibers.

B. Tight Phase

A tight phase in filter medium 10 typically includes a third pluralityof fibers and a fourth plurality of fibers.

In some embodiments, the third plurality of fibers can have the samecharacteristics (e.g., air permeability and/or pressure drop) or be madefrom the same type of material as the first or second plurality offibers described above, and the fourth plurality of fibers can have thesame characteristics or be made from the same type of material as thefirst or second plurality of fibers described above.

In some embodiments, the third plurality of fibers can have one or morecharacteristics (e.g., air permeability and/or pressure drop), or bemade from a type of material, different from those of the first orsecond plurality of fibers, and the fourth plurality of fibers can haveone or more characteristics, or be made from a type of material,different from those of the first or second plurality of fibers.

In some embodiments, a tight phase can include a mixture of softwoodfibers and hardwood fibers. In certain embodiments, the tight phase caninclude only one type of fibers (e.g., hardwood fibers) uniformlydistributed within the tight phase.

In some embodiments, a tight phase can include a mixture of fibers withdifferent characteristics (e.g., different air permeabilities and/orpressure drops). Fibers with different characteristics can be made fromone material (e.g., by using different process conditions) or differentmaterials.

In some embodiments, the third plurality of fibers can be formed from amaterial identical to the material used to form the fourth plurality offibers. In such embodiments, the third and fourth pluralities of fiberscan be prepared by using different preparation methods, or differentconditions in the same preparation method, such that they have differentcharacteristics (e.g., different air permeability or pressure drop). Incertain embodiments, the third and fourth pluralities of fibers can beformed of the same material and also have the same characteristics. Insome embodiments, the third plurality of fibers can be formed from amaterial different from the material used to form the fourth pluralityof fibers.

Generally, the weight ratio of the third and fourth plurality of fiberscan vary depending on the desired properties of filter medium 10 or itsintended uses. A tight phase in filter medium 10 typically includesfibers with a higher air permeability and/or a smaller pressure drop inan amount smaller than the amount of fibers with a smaller airpermeability and/or a larger pressure drop. For example, a weight ratioof the third and fourth pluralities of fibers described above can rangefrom about 3:97 to about 50:50 (e.g., from about 25:75 to about 50:50 orfrom about 70:30 to about 50:50). As used herein, the weight of thethird or fourth plurality of fibers refers to the initial weight of eachgroup of fibers in a composition (e.g., a pulp) used to prepare thetight phase. In some embodiments, a tight phase in filter medium 10 caninclude fibers with a higher air permeability and/or a smaller pressuredrop in an amount larger than or equal to the amount of fibers with asmaller air permeability and/or a larger pressure drop.

In some embodiments, a tight phase can include one or more pluralitiesof fibers in addition to the third and fourth pluralities of fibers.Each of the additional pluralities of fibers can have characteristics(e.g., air permeability or pressure drop) different from the third orfourth plurality of fibers, or can be prepared from a material differentfrom those used to prepare the third or fourth plurality of fibers. Insome embodiments, an additional plurality of fibers can be prepared froma material identical to a material used to form one of the third andfourth pluralities of fibers, but still have characteristics differentfrom those of the third or fourth plurality of fibers.

In general, the weight ratio of the open and tight phases in filtermedium 10 can vary as desired. For example, a basis weight ratio of theopen and tight phases can range from about 10:90 to about 90:10 (e.g.,from about 30:70 to about 70:30, from about 40:60 to about 60:40, orfrom about 30:70 to about 90:10). In certain embodiments, the basisweight ratio of the open and tight phases is about 30:70 or greater(e.g., about 40:60 or greater, about 50:50 or greater, or about 60:40 orgreater). As used herein, basis weight of an open or tight phase refersto the weight of the phase over a unit area (e.g., per square meter).For example, the basis weight of an open or tight phase can have a unitof grams per square meter.

C. Filter Medium Properties

In general, the thickness of filter medium 10 can vary as desired. Forexample, filter medium 10 can have a thickness from 100 microns to 2,000microns (e.g., from 300 microns to 1,000 microns or from 400 microns to750 microns). The thickness may be determined according to the standardTAPPI T411.

Generally, filter medium 10 can have any desired basis weight. Forexample, filter medium 10 can have a basis weight of at least about 10g/m² (e.g., at least about 50 g/m² or at least about 100 g/m²) and/or atmost about 500 g/m² (e.g. at most about 250 g/m² or at most about 200g/m²). As used herein, basis weight of a filter medium refers to theweight of the medium over a unit area (e.g., per square meter). Atypical unit for the basis weight is g/m².

The air permeability of filter medium 10 can usually be selected asdesired. For example, the air permeability of filter medium 10 can be atleast about 2 CFM (e.g., at least about 5 CFM, at least about 10 CFM, orat least about 30 CFM) and/or at most about 200 CFM (e.g., at most about160 CFM, at most about 120 CFM, or at most about 80 CFM). As usedherein, air permeability of a filter medium is determined according toISO 9237.

The average pore size of filter medium 10 can vary as desired. Forexample, filter medium 10 can have an average pore size from at leastabout 3 microns (e.g., at least about 10 microns, at least about 25microns, or at least about 100 microns) and/or at most about 1,000microns (e.g., at most about 500 microns, or at most about 125 microns).As used herein, the average pore size refers to the mean flow pore sizemeasured by using a Coulter Porometer as described in ASTM F316-03.

Filter medium 10 can exhibit good ability to capture dust. For example,filter medium 10 can have an initial dust capture efficiency of at leastabout 25% (e.g., at least about 60%, at least about 80%, at least about85%, or at least about 90%) and/or at most about 99.5% (e.g., at mostabout 98% or at most about 95%) measured according to a Palas flat sheettest. A description of the Palas flat sheet test used to determine aninitial dust capture efficiency is provided in the test protocol sectionbelow.

Filter medium 10 can also have good dust holding properties. Forexample, filter medium 10 can have a dust holding capacity (DHC) of atleast about 0.3 g (e.g., at least about 1 g or at least about 2 g)and/or at most about 3 g (e.g., at most about 2.5 g or at most about 2g) according to a Palas flat sheet test. A description of the Palas flatsheet test to determine a dust holding capacity is provided in the testprotocol section below. As another example, filter medium 10 can have aspecific dust holding capacity of at least about 0.001 g/g (e.g., atleast about 0.004 g/g) and/or at most about 1.0 g/g (e.g., at most about0.9 g/g). As used herein, specific dust holding capacity can becalculated by dividing a DHC of a filter medium over a unit weight(e.g., per gram) of the filter medium. Alternatively, specific dustholding capacity can be calculated by dividing a DHC of a filter mediumover a unit thickness (e.g., per millimeter) of the filter medium.

In some embodiments, filter medium 10 has both good dust capture andgood dust holding properties. As an example, filter medium 10 can havean initial dust capture efficiency of at least about 25% (e.g., at leastabout 60%, at least about 80%, at least about 85%, or at least about90%) and a dust holding capacity of at least about 0.3 g (e.g., at leastabout 1 g or at least about 2 g).

In some embodiments, at least one of the first, second, third, andfourth pluralities of fibers described above are made from an organicpolymeric material (e.g., softwood fibers, cotton fibers, hardwoodfibers, or synthetic organic polymers such as polyester or rayon). Incertain embodiments, more than one (e.g., two, three, or all) of thefirst, second, third and fourth pluralities of fibers are made from anorganic polymeric material.

In some embodiments, filter medium 10 can further include a binderdistributed throughout the filter medium. In general, including a binderin a filter medium can significantly increase its strength (e.g.,tensile strength measured according to ISO 1924-2 or Mullen Burststrength measured according to DIN 53113). The binder can include apolymeric material, such as polyvinyl acetate, an epoxy, a polyester, apolyvinyl alcohol, an acrylic (e.g., a styrene acrylic), or a phenolicresin. In some embodiments, the binder can be at least about 2% and/orat most about 35% (e.g., at most about 25%, at most about 15%, or atmost about 5%) of the basis weight of filter medium 10. In general, thebinder can be present in filter medium 10 with out without the presenceof cross-linking agents (e.g., melamine, hexamine, or an epoxy hardener)or other additives (e.g., silicones, fluorocarbons, or catalysts such asammonium chloride).

Filter medium 10 typically includes an interface between first phase 12and second phase 16. In some embodiments, when filter medium 10 isprepared in a continuous wet laid process (e.g., forming first phase 12and second phase 16 in a continuous liquid-based coating process), theinterface can take the form of a transition phase which includes atleast a portion of each of the first, second, third, and fourthpluralities of fibers intermingled with each other. Without wishing tobe bound by theory, it is believed that the interface in filter medium10 prepared by such a process can be substantially non-linear due to theinteraction between the fibers in first phase 12 and second phase 16.For example, FIG. 4 shows a scanning electron microscope graph of a dualphase filter medium, in which the interface is substantially non-linear.Further, as no adhesive is typically used in a wet laid process, theinterface is typically substantially free of any adhesive. First andsecond phases which include an interface that is substantially free ofan adhesive may be joined by, for example, physical interactions betweenthe fibers in each of the phases, or by other suitable methods that donot involve the use of an adhesive to join the phases. In some cases,first and second phases which include an interface that is substantiallyfree of an adhesive are not joined by lamination.

In some embodiments, filter medium 10 can include one or more phases inadditional to first phase 12 and second phase 16. An additional phasecan be the same as or different from first phase 12 or second phase 16.

II. Filter Elements and Systems

Filter element 100 can be any of a variety of filter elements. Examplesof filter elements include gas turbine filter elements, dust collectorelements, heavy duty air filter elements, automotive air filterelements, HVAC air filter elements, HEPA filter elements, vacuum bagfilter elements, fuel filter elements, and oil filter elements (e.g.,lube oil filter elements or heavy duty lube oil filter elements).

Filter element 100 can also be in any suitable form, such as radialfilter elements, panel filter elements, or channel flow elements. Aradial filter element can include pleated filter media that areconstrained within two open wire meshes in a cylindrical shape. Duringuse, fluids can flow from the outside through the pleated media to theinside of the radial element.

When filter element 100 is a heavy duty air filter element, each of theopen and tight phases in a single filter medium 10 can include a mixtureof softwood fibers (e.g., Robur Flash fibers) and hardwood fibers (e.g.,Suzano fibers). The weight ratio of the open and tight phases can beabout 30:70 or greater. The weight ratio of the softwood fibers andhardwood fibers in the open phase can be, for example, about 85:15, andthe weight ratio of the softwood fibers and hardwood fibers in the tightphase can be, for example, about 49:51.

When filter element 100 is an automotive air filter element, each of theopen and tight phases in a single filter medium 10 can include a mixtureof softwood fibers and hardwood fibers (e.g., Suzano fibers). The weightratio of the open and tight phases can be about 50:50. The weight ratioof the softwood fibers and hardwood fibers in the open phase can beabout 93:7, and the weight ratio of the softwood fibers and hardwoodfibers in the tight phase can be about 65:35. Each of the open and tightphases can be made from two types of different softwood fibers (e.g.,Robur Flash fibers and HPZ fibers). The weight ratio of the two types ofdifferent softwood fibers in the open phase can be about 83:10 (e.g.,about 83% mercerized southern pine fibers and about 10% of Robur Flashfibers). The weight ratio of the two types of different softwood fibersin the tight phase can be about 40:25 (e.g., about 40% HPZ fibers andabout 25% of Robur Flash fibers).

When filter element 100 is a fuel filter element, each of the open andtight phases in a single filter medium 10 can include a mixture ofsoftwood fibers and hardwood fibers. The weight ratio of the open andtight phases can be about 50:50. The weight ratio of the softwood fibersand hardwood fibers in the open phase can be about 60:40, and the weightratio of the softwood fibers and hardwood fibers in the tight phase canbe about 6:94. The open phase can be made from two types of differentsoftwood fibers with a weight ratio of about 40:20 (e.g., about 40% HPZfibers and about 20% of Robur Flash), and a type of hardwood fibers(e.g., about 40% of Suzano fibers). The tight phase can be made of threetypes of different hardwood fibers with a weight ratio of about 48:36:10(e.g., about 48% Suzano fibers, about 36% of Tarascon fibers, and about10% Acacia fibers) and a type of softwood fibers (e.g., about 6% HPZfibers).

The orientation of filter medium 10 relative to gas flow through afilter element/filter system can generally be selected as desired. Insome embodiments, second phase 16 is upstream of first phase 12 in thedirection of gas flow through a filter element. In certain embodiments,second phase 16 is downstream of first phase 12 in the direction of gasflow through a filter element. As an example, when the gas filterelement is a gas turbine filter element or a heavy duty air filterelement, second phase 16 can be upstream of first phase 12 in thedirection of gas flow through the filter element. As another example,when improved depth filtration is desired, second phase 16 can bedownstream of first phase 12 in the direction of gas flow through thefilter element.

III. Methods of Manufacturing Filter Medium

In general, filter medium 10 can be made by any suitable methods.

In some embodiments, filter medium 10 can be prepared by a wet laidprocess as follows: First, a first dispersion (e.g., a pulp) containingfirst and second pluralities of fibers in a solvent (e.g., an aqueoussolvent such as water) can be applied onto a wire conveyor in apapermaking machine (e.g., a fourdrinier or a rotoformer) to form firstphase 12 supported by the wire conveyor. A second dispersion (e.g.,another pulp) containing third and fourth pluralities of fibers in asolvent (e.g., an aqueous solvent such as water) is then applied ontofirst phase 12. Vacuum is continuously applied to the first and seconddispersions of fibers during the above process to remove the solventfrom the fibers, thereby resulting in an article containing first phase12 and second phase 16. The article thus formed is then dried and, ifnecessary, further processed (e.g., calendered) by using known methodsto form multi-phase filter medium 10. In some embodiments, first phase12 and second phase 16 in a multi-phase filter medium 10 do not havemacroscopic phase separation as shown in a conventional multi-layerfilter medium (e.g., where one layer is laminated onto another layer inthe filter medium), but instead contain an interface in whichmicroscopic phase transition occurs depending on the fibers used or theforming process (e.g., how much vacuum is applied).

In some embodiments, a polymeric material can be impregnated into filtermedium 10 either during or after filter medium 10 is being manufacturedon a papermaking machine. For example, during the manufacturing processdescribed above, after the article containing first phase 12 and secondphase 16 is formed and dried, a polymeric material in a water basedemulsion or an organic solvent based solution can be adhered to anapplication roll and then applied to the article under a controlledpressure by using a size press or gravure saturator. The amount of thepolymeric material impregnated into filter medium 10 typically dependson the viscosity, solids content, and absorption rate of filter medium10. As another example, after filter medium 10 is formed, it can beimpregnated with a polymeric material by using a reverse roll applicatorfollowing the just-mentioned method and/or by using a dip and squeezemethod (e.g., by dipping a dried filter media into a polymer emulsion orsolution and then squeezing out the excess polymer by using a nip). Apolymeric material can also be applied to filter medium 10 by othermethods known in the art, such as spraying or foaming.

In general, filter medium 10 can be prepared by a continuousmanufacturing process (e.g., a roll-to-roll manufacturing process) orcan be prepared in a non-continuous, batch-to-batch manner.

The following examples are illustrative only and not intended aslimiting.

IV. Examples

A. Test Protocols:

Initial Dust Capture Efficiency and Dust Holding Capacity

A 100 cm² surface area of a filter medium was challenged with a finedust (0.1-80 μm) at a concentration of 200 mg/m³ with a face velocity of20 cm/s for one minute. The dust capture efficiency was measured using aPalas MFP2000 fractional efficiency photodetector. The dust captureefficiency was [(1−[C/C0])*100%], where C was the dust particleconcentration after passage through the filter and C0 was the particleconcentration before passage through the filter. The dust captureefficiency was measured after one minute and is referred to herein asthe initial dust capture efficiency. The dust holding capacity ismeasured when the pressure reaches 1,800 Pa, and is the difference inthe weight of the filter medium before the exposure to the fine dust andthe weight of the filter medium after the exposure to the fine dust.This test is referred to herein as a Palas flat sheet test.

Liquid Filtration Efficiency Test and Liquid Filtration RetentionEfficiency

Using a FTI Multipass Filter Test Stand (Fluid Technologies Inc.,Stillwater, Okla.), an A2 fine dust is fed at a rate of 0.3 liters perminute into Mobil MIL-H-5606 fuel for a total flow rate of 1.7 litersper minute to contact a filter medium per ISO 16889 until a terminalpressure of 174 KPa above the baseline filter pressure drop is obtained.Particle counts (particles per milliliter) are taken at the particlesized selected (in this case 4, 5, 7, 10, 15, 20, 25 and 30 microns).The particle counts are taken upstream and downstream of the media atten points equally divided over the time of the test. The average ofupstream and downstream particle counts are taken at each selectedparticle size. From the average particle count upstream (injected −C₀)and the average particle count downstream (passed thru-C) the liquidfiltration efficiency test value for each particle size selected isdetermined by the relationship [(100−[C/C₀])*100%]. The liquidfiltration retention efficiency as a function of time and particle sizecan also be measured by comparing the upstream and downstream particlecounts (and determining efficiency [(100−[C/C0])*100%]) at thesequential ten points in the test. This test is referred to herein as amulti-pass flat sheet test.

B. Examples Example 1

Single phase and dual phase filter media were prepared on a trial papermachine (TPM). The single phase filter media were prepared using a blendof HPZ fibers and Suzano fibers. The weight ratios of the HPZ fibers andSuzano fibers in the blend were 90/10, 70/30, and 50/50, respectively.The dual phase filter media were prepared using HPZ fibers to form anopen phase and Suzano fibers to form a tight phase, in which the weightratios of the HPZ fibers and Suzano fibers were also 90/10, 70/30, and50/50, respectively. To form a dual phase filter medium, a flowseparation insert was used to separate the pulp containing HPZ fibersfrom the pulp containing Suzano fibers. The open phase was formed on thebottom of a dual phase filter medium and the tight phase was formed atthe top. The dual phase filter media thus formed had a densityequivalent to the single phase filter media. Both the single and dualphase filter media were not saturated with a resin for improving thestrength of the media.

The filter media were refined by passing the pulps used to form thefilter media twice through a refiner with a load energy of 35 Amps tomeet specific air permeability target for each grade. Each type offilter medium was replicated three times. The filter media were thentested for their capacity performance using a Palas air stand accordingto the Palas flat sheet test described above, tested for their MullenBurst strength according to DIN 53113, and tested for their tensilestrength according to ISO 1924-2.

The results showed that the dual phase filter media exhibited from 30%to 100% increase in their specific dust holding capacity (DHC) comparedto the single phase filter media. The results also showed that the dualphase filter media exhibited about 20% loss in strength compared to thesingle phase filter media.

Example 2

Three types of automotive air filter media (i.e., filter media 1, 2, and3) in both single phase and dual phase of a sufficient size to allow forsaturation and element testing were produced on a fourdrinier in amanner similar to that described in Example 1.

The single phase filter media were prepared using a blend of fibers.Specifically, single phase filter media 1 contained a blend of about 47wt % of HPZ fibers and about 53 wt % of Cacia fibers, single phasefilter media 2 contained a blend of about 70 wt % HPZ fibers and about30 wt % of Suzano fibers, and single phase filter media 3 contained ablend of about 81 wt % HPZ fibers, about 9.5 wt % Leaf River fibers, andabout 9.5 wt % Cacia fibers.

The dual phase filter media were prepared using HPZ fibers to form anopen phase and Suzano, Cacia, or Leaf River fibers to form a tightphase. Specifically, dual phase filter media 1 contained about 47 wt %of HPZ fibers in the open phase and about 53 wt % of Cacia fibers in thetight phase, dual phase filter media 2 contained about 70 wt % HPZfibers in the open phase and about 30 wt % of Suzano fibers in the tightphase, and dual phase filter media 3 contained about 81 wt % HPZ fibersin the open phase, and about 9.5 wt % Leaf River fibers and about 9.5 wt% Cacia fibers in the tight phase.

The above filter media were subsequently saturated with an epoxy resinby using an impregnation machine. The filter media were refined in thesame manner as described in Example 1 to meet specific air permeabilitytarget for each grade.

Panel air elements and cylindrical elements containing each type offilter medium were produced. Specifically, a panel air element wasproduced by assembling a pleated filter medium between a molded siliconeelastomer which holds the filter medium around the edges. A cylindricalelement was produced by wrapping a pleated medium around a center tube,placing the article thus formed into a can, and sealing the can. Thepanel air element is generally used for high CFM automotive air, whilethe cylindrical element is generally used for low CFM heavy duty Air.

The performance of panel air elements was measured according to astandard method SAE J726. The results showed that elements containingthe dual phase filter media exhibited an average 25% increase in DHCcompared to elements containing the single phase filter media. Elementscontaining the dual phase filter media also exhibited about 3% increasein initial dust capture efficiency.

The performance of cylindrical elements was also measured according tothe standard method SAE J726. Elements containing the dual phase filtermedia exhibited an average of 7% increase in overall DHC compared toelements containing the single phase filter media.

Mullen Burst and tensile strength of the single phase and dual phasefilter media prepared above were measured. The results showed that thedual phase filter media exhibited a reduction in strength compared tothe single phase filter media. The impact of the reduction was howeverless after the filter media was saturated with the epoxy resin. TheMullen Burst strength of the dual phase filter media was an average ofabout 80% of that of the single phase filter media depending upon thegrade. Tensile strength comparisons between the two types of filtermedia showed a similar trend. In all cases, enough strength was presentto effectively process the dual phase filter media.

Example 3

An interlayer design was used to produce dual phase filter media 4 usinga rotoformer. As used herein, an interlayer design refers to a designthat include a mixture of fibers with different characteristics in oneor both of the open and tight phases. Specifically, dual phase filtermedia 4 contained about 45 wt % bottom phase (a tight phase) thatincluded about 72 wt % Suzano fibers and about 28 wt % Robur Flashfibers, and about 55 wt % top phase (an open phase) that included about15 wt % Suzano fibers and about 85 wt % Robur Flash fibers. Single phasefilter media 4 were produced using about 40 wt % of Suzano fibers andabout 60 wt % Robur Flash fibers. The performance of the filter mediathus prepared are summarized in Table 1. Each value is an average ofthree tests per sample. After the filter media were formed, they werecorrugated by compressing the media between two grooved corrugator rollsusing sufficient pressure to result in machine directional grooves orcorrugations in the filter media.

As shown in Table 1, dual phase filter media 4 exhibited significantimprovement in DHC (about 26%) and specific DHC (from about 14-33%)compared to single phase filter media 4 when measured using the Palasflat sheet test described above. Further, dual phase filter media 4showed little strength degradation compared to single phase filter media4. It is believed that the interlayer design effectively addressed thestrength loss issue observed in Examples 1 and 2.

TABLE 1 Single Dual phase filter phase filter media 4 media 4 UnitsBasis weight 115 108 g/m² (average) Basis weight 110 102 g/m² (min.)Basis weight 120 115 g/m² (max.) Basis weight 70.7 66.4 lbs./3000 ft²Caliper 0.55 0.62 mm @2N/cm² (average) Caliper 0.53 0.5 mm @2N/cm²(min.) Caliper 0.59 0.85 mm @2N/cm² (max.) Caliper 21.7 24.4 milsCorrugation depth 0.21 0.22 mm @ 1.76 N/cm² Air resistance 7.44 7.92mbar @ 40 cm/s Air permeability 135 130 1/s m² @ 200 Pa Air permeability17.0 16.3 cfm @ ½″WG max. pore 44.3 39.3 μm (IPA) many pores 33.7 33.7μm (IPA) Burst strength 267 235 kPa Burst strength 38.7 34.1 psi Tensile89 78 N/15 mm strength MD Tensile 60 43.4 N/15 mm strength CD CD/MDratio 1.48 1.80 CD = 1:MD Tensile 33.2 29.1 lbs/inch strength MD Tensile22.4 16.2 lbs/inch strength CD Elongation 4.1 3 % Elongation 10 7.3 %Initial 390 438 Pa Pressure Drop Initial 94.7 94.9 % Efficiency Final100 100 % Efficiency Dust Holding 0.76 0.96 g Capacity, DHC SpecificDHC - 0.33 0.44 g dust/g media g/g Specific DHC- 1.36 1.55 g dust/mmmedia g/mm

Example 4

An interlayer approach was used to produce unsaturated single and dualphase filter media 5, 6, and 7 using a rotoformer.

Single phase (SP) filter media 5 contained a blend of about 28 wt % HPZfibers, about 48 wt % Cacia fibers, and about 30 wt % Robur Flashfibers. Dual phase (DP) filter media 5 contained about 50 wt % of atight phase and about 50 wt % of an open phase. The tight phase includedabout 12 wt % HPZ fibers, about 68 wt % Cacia fibers, and about 20 wt %Robur Flash fibers. The open phase included about 40 wt % HPZ fibers,about 30 wt % Cacia fibers, and about 30 wt % Robur Flash fibers.

Single phase filter media 6 contained a blend of about 58.2 wt % HPZfibers and about 41.8 wt % of Suzano fibers. Dual phase filter media 6contained 80 wt % of a tight phase and about 20 wt % of an open phase.The tight phase included about 52 wt % HPZ fibers, about 48 wt % Suzanofibers. The open phase included about 83 wt % HPZ fibers, about 17 wt %Robur Flash fibers.

Single phase filter media 7 contained a blend of about 24.5 wt %polyester fibers, about 43.7 wt % HPZ fibers, about 28.9 wt % Suzanofibers, and about 3 wt % CTMP fibers. Dual phase filter media 7contained about 70 wt % of a tight phase and about 30 wt % of an openphase. The tight phase included about 26 wt % polyester fibers, about 37wt % HPZ fibers, and about 37 wt % of Suzano fibers. The open phaseincluded about 21 wt % polyester fibers, about 59 wt % HPZ fibers, about10 wt % Suzano fibers, and about 10 wt % CTMP fibers.

The performance of the filter media thus prepared are summarized inTable 2. Each value is an average of three tests per sample.

TABLE 2 SP 5 DP 5 SP 6 DP 6 SP 7 DP 7 unit Basis weight 97 103 119 115115 127 g/m² (average) Basis weight 97 101 118 111 113 125 g/m² (min.)Basis weight 98 105 121 122 116 130 g/m² (max.) Basis weight 59.6 63.373.1 70.7 70.7 78.1 lbs./3000 ft² Caliper 0.47 0.66 0.69 0.64 0.75 0.91mm @2N/cm² (average) Caliper 0.46 0.5 0.67 0.58 0.72 0.61 mm @2N/cm²(min.) Caliper 0.49 0.91 0.72 0.67 0.8 1.27 mm @2N/cm² (max.) Caliper18.5 26.0 27.2 25.2 29.6 35.9 mils Corrugation depth 0 0 0 0 0 0 mm @1.76 N/cm² Air resistance 4.82 6.54 2.28 2.38 1.27 1.52 mbar @ 40 cm/sAir permeability 198 156 400 387 701 605 l/s m² @ 200 Pa Airpermeability 25.1 19.7 51.4 49.7 91.2 78.4 cfm @ ½″WG max. pore 46 45.262.4 65.2 78.7 67.2 μm (IPA) many pores 40 34.9 54.9 52.9 70.4 61.9 μm(IPA) Burst strength 77 73 55 57 49 46 kPa Burst strength 11.2 10.6 8.08.3 7.1 6.7 psi Tensile strength MD 22.5 25.6 16.1 16.7 11.5 11.9 N/15mm Tensile strength CD 18.4 17.3 11.6 11.3 7.6 8.1 N/15 mm CD/MD ratio1.22 1.48 1.39 1.48 1.51 1.47 CD = 1:MD Tensile strength MD 8.4 9.6 6.06.2 4.3 4.4 lbs/inch Tensile strength CD 6.9 6.5 4.3 4.2 2.8 3.0lbs/inch Elongation 1.2 1.4 1.6 1.2 1.2 1.1 % Elongation 1.6 2.8 2.5 2.81.6 1.6 % Initial Pressure Drop 249 333 104 118 Pa Initial Efficiency93.3 96.6 78 82.5 % Final Efficiency 100 100 100 99.8 % Dust HoldingCapacity, DHC 1.1 1.37 1.88 2.07 5.51* 5.05* g Specific DHC - g/g 0.560.66 0.79 0.9 g dust/g media Specific DHC- g/mm 2.34 2.07 2.72 3.23 1.6*g dust/mm media *These values were measured by using a multi-pass flatsheet test.

As shown in Table 2, the dual phase filter media exhibited significantimprovement in DHC when measured using the PALAS flat sheet testdescribed above.

Example 5

Dual phase and single phase filter media were produced to targetspecifications using a rotoformer. Specifically, the following filtermedia were produced in the same manner as that described in Examples 3and 4: (1) dual phase filter media 8, 9, and 10, and (2) single phasefilter media 12 and 13 as controls. An interlayer approach was used toproduce dual phase filter media. The compositions of these dual phaseand single phase filter media are summarized in Table 3 below. In thedual phase filter media, the bottom phase was a tight phase and the topphase was an open phase.

TABLE 3 Single SP 12 SP 11 phase (SP) Robur Flash - 60 wt % RoburFlash - 32.5 wt % Suzano - 40 wt % Suzano - 29 wt % Westvaco HW - 38.5wt % Dual DP 8 DP 9 DP 10 phase (DP) Bottom Phase - 70 wt % BottomPhase - 70 wt % Bottom Phase - 70 wt % Robur Flash - 49 wt % RoburFlash - 43 wt % Robur Flash - 10 wt % Suzano - 51 wt % Suzano - 57 wt %Suzano - 35 wt % Top Phase - 30 wt % Top Phase - 30 wt % Westvaco HW -55 wt % Robur Flash - 85 wt % Robur Flash - 100 wt % Top Phase - 30 wt %Suzano - 15 wt % Suzano - 0 wt % Robur Flash - 85 wt % Suzano - 15 wt %

The performance of these filter media were measured using the Palas flatsheet test described above. The results are summarized in Table 4 below.

TABLE 4 Initial Final Initial Specific Specific Trial EfficiencyEfficiency DP DHC DHC DHC # (%) (%) (Pa) (g) (g/g) (g/mm) DP 8 88.5099.99 415 1.352 0.60725 4.9746 DP 9 92.13 99.99 438 1.000 0.45514 3.1073DP 10 91.84 100.00 465 1.064 0.50212 3.4908 SP 11 92.07 100.00 451 0.9200.42112 2.9376 SP 12 90.11 100.00 421 0.824 0.36320 2.7034

As shown in Table 4, DP 8 and DP 9 exhibited at least 20% improvement inDHC and at least 15% improvement in specific DHC compared to SP 12. DP10 also exhibited about 10% improvement in DHC and about 17% improvementin specific DHC compared to SP 11.

The strength of the filter media above were also tested. The resultsshowed that the strength of the dual phase filter media was about 10%lower than that of the single phase filter media, and was moresignificant for DP10 as compared to SP11.

Example 6

Additional testing of DP 8 and SP 12 prepared in Example 5 were carriedout as follows.

High pressure flat sheet testing of DP 8 and SP 12 were carried outusing the Palas flat sheet test described above except that a higherterminal pressure of 4,500 Pa was applied. The results are summarized inTable 5 below. As shown in Table 5, DP 8 exhibited at least about 40%improvement in DHC and specific DHC compared to SP 12.

TABLE 5 Initial Initial Final Specific Specific Trial dP Eff. Eff. DHCDHC/mm DHC/g Type # (Pa) (%) (%) (g) (g/mm) (g/g) Single phase SP 12 38389.3 100 2.06 2.75 0.91 Dual phase DP 8 379 84.8 100 2.87 4.33 1.29

DP 8 and SP 12 were incorporated into radial filter elements and testedusing a radial element test designed to simulate heavy duty air facevelocity of 8 ft/min. Compared to elements containing SP 12, elementscontaining DP 8 exhibited about 23% improvement in DHC and specific DHCcalculated based on per square meter of a filter medium.

Example 7

A series of short trials were completed using a TPM to optimize the DHCof dual phase filter media. Filter media 13, 14, 15, 16, and 17 wereproduced. For each type of filter media, a single phase version (i.e.,SP) and two dual phase versions (i.e., DP1 and DP2) were produced. Forfilter media 14, an addition dual phase version (i.e., DP2vv) with atight phase at the bottom was produced. All of the dual phase filtermedia were produced by an interlayer design. The compositions of thesefilter media are summarized in Table 6 and the performance of the filtermedia are summarized in Tables 7 and 8.

TABLE 6 Filter media 13 Filter media 14 Filter media 15 Filter media 16Filter media 17 (wt %) (wt %) (wt %) (wt %) (wt %) Single HPZ - 28%HPZ - 71% Polyester - 23% HPZ - 64% HPZ - 19% phase Cacia - 48% Suzano -29% HPZ - 49% Brunswick Pine - 26% Suzano - 63% (SP) Robur Flash - 24%Suzano - 22% Cacia - 10% Tarascon - 18% CTMP - 6% Dual Open Phase - 50%Open Phase - 50% Open Phase - 50% Open Phase - 50% Open Phase - 50%phase HPZ - 40% HPZ - 83% HPZ - 60% HPZ - 85% HPZ - 35% (DP1) Cacia -20% Suzano - 17% Polyester - 30% Brunswick Pine - 10% Suzano - 65% RoburFlash - 40% Tight Phase - 50% Suzano - 10% Cacia - 5% Tight Phase - 50%Tight Phase - 50% HPZ - 60% Tight Phase - 50% Tight Phase - 50% HPZ -10% HPZ - 0% Suzano - 40% HPZ - 32% HPZ - 42.5% Suzano - 54% Cacia - 68%Polyester - 16% Brunswick Pine - 42.5% Tarascan - 36% Robur Flash - 32%Suzano - 32% Cacia - 15% CTMP - 20% Dual Open Phase -50% Open Phase -50%Open Phase - 50% Open Phase - 70% Open Phase - 50% phase HPZ - 56% HPZ -83% HPZ - 50% HPZ - 87% HPZ - 40% (DP2) Cacia - 30% Suzano - 7%Polyester - 30% Brunswick Pine - 13% Suzano - 50% Robur Flash - 14%Robur Flash - 10% Robur Flash - 20% Tight Phase - 30% Robur Flash - 10%Tight Phase - 50% Tight Phase - 50% Tight Phase - 50% HPZ - 9% TightPhase - 50% HPZ - 0% HPZ - 40% HPZ - 32% Brunswick Pine - 55% Suzano -54% Cacia - 68% Suzano - 35% Polyester - 16% Cacia - 36% Tarascan - 36%Robur Flash - 32% Robur Flash - 25% Suzano - 32% Acacia - 10% RoburFlash - 20%

TABLE 7 Multipass test results Palas efficiency efficiency g/m² mm @l/m²s @ Burst initial initial DHC 50% 90% DHC Samples [g/m²] 2 N/cm² 200Pa Strength efficiency pressure [mg/cm²] [μm] [μm] [g/200 cm²] Filter SP119 0.60 507 90 63.9 107 8.36 media DP 1 117 0.59 494 83 72.4 83 7.88 14DP 2 117 0.58 507 72 59.2 84 9.56 DP 2w 109 0.56 514 77 69.6 95 11.96Filter DP 1 105 0.43 125 138 87.2 319 8.12 media DP 2 108 0.47 160 12089 319 7.88 13 SP 107 0.45 176 132 89.1 319 6.44 Filter DP 1 119 0.64608 50 18.1 26.6 3.72 media DP 2 121 0.66 627 60 20.3 30.1 4.91 15 SP124 0.67 662 56 20.6 31.2 4.26 Filter DP 1 162 0.81 396 118 19.2 30 4.28media DP 2 164 0.80 355 71 18.3 26.4 4.25 16 SP 164 0.79 403 132 20.630.2 3.57 Filter DP 1 186 0.45 19 299 media DP 1 187 0.43 16 319 3.75.25 0.62 17 DP 2 181 0.45 15 280 4 5.5 0.6 SP 189 0.47 16 288 4 5.50.38

TABLE 8 Single Dual Phase Phase 2 DHC Grade DHC/g DHC/g increase/%Filter media 14 8.36 11.96 43.06 Filter media 13 6.44 7.88 22.36 Filtermedia 15 4.26 4.91 15.26 Filter media 16 3.57 4.25 19.05 Filter media 170.38 0.60 57.89

As shown in Tables 7 and 8, interlayer designs in the dual phase filtermedia showed positive results (i.e., with significantly improved DHC andstrength properties maintained) as compared to the single phase filtermedia. The DP2 version of each type of filter media yielded the mostimprovement in DHC compared to its corresponding single phase control.In filter media 14, DP2vv, which contained a tight phase on the bottom,showed a 43% improvement in DHC. This approach appeared to yield thehighest DHC improvement.

Example 8

Trial production was carried out to optimize dual phase filter mediaprepared in Example 7. Specifically, optimized versions of filter media13 (for use in a heavy duty air filter element), 14 (for use in anautomotive air filter element), 15 (for use in lube oil filter element),16 (for use in a heavy duty lube oil filter element), and 17 (for use ina fuel filter element) were produced. For each type of filter media, asingle phase version and a dual phase version of each grade of filtermedia were produced. A fourdrinier and an impregnator were used toproduce single and dual phase filter media, which were saturated with asolvent based phenolic resin. All dual phase filter media were producedwith a tight phase on the bottom using an interlayer design. Thecompositions of these filter media are summarized in Table 9 and theperformance of the filter media are summarized in Tables 10 and 11.

TABLE 9 Filter media 13 Filter media 14 Filter media 15 Filter media 16Filter media 17 (wt %) (wt %) (wt %) (wt %) (wt %) Single HPZ - 28%HPZ - 71% Polyester - 23% HPZ - 64% HPZ - 19% phase Cacia - 48% Suzano -29% HPZ - 49% Brunswick Pine - 26% Suzano - 63% Robur Flash - 24%Suzano - 22% Cacia - 10% Tarascon - 18% CTMP - 6% Dual Open Phase - 50%Open Phase - 50% Open Phase - 50% Open Phase - 50% Open Phase - 50%phase HPZ - 56% HPZ - 83% HPZ - 50% HPZ - 85% HPZ - 40% Cacia - 30%Suzano - 7% Polyester - 30% Brunswick Pine - 10% Suzano - 40% RoburFlash - 14% Robur Flash - 10% Robur Flash - 20% Cacia - 5% Robur Flash -20% Tight Phase - 50% Tight Phase - 50% Tight Phase - 50% Tight Phase -50% Tight Phase - 50% HPZ - 0% HPZ - 40% HPZ - 32% HPZ - 42.5% HPZ - 6%Cacia - 68% Suzano - 35% Polyester - 16% Brunswick Pine - 42.5% Suzano -48% Robur Flash - 32% Robur Flash - 25% Suzano - 32% Cacia - 15%Tarascan - 36% Robur Flash - 20% Acacia - 10%

TABLE 10 Palas Flat Sheet Test Results Initial Specific SpecificEfficiency DHC DHC DHC Samples (%) (g) (g/g) (g/mm) Filter media 13Single phase 87.5 0.60 0.46 1.36 Dual phase 87.2 0.44 0.62 1.73 Dualphase change (%) −0.3 28.57 33.15 27.32 Filter media 14 Single phase58.1 0.76 0.54 1.38 Dual phase 59.4 1.04 0.73 1.76 Dual phase change (%)2.2 36.84 35.77 27.93

TABLE 11 Multi-pass flat sheet Test Results Initial Specific SpecificEfficiency DHC DHC DHC Samples (%) (g) (g/g) (g/mm) Filter media 15Single phase 13.0 4.28 1.43 6.47 Dual phase 18.5 5.24 1.91 8.04 Dualphase change (%) 42.3 22.6 33.6 24.3 Filter media 16 Single phase 22.53.60 0.90 4.94 Dual phase 17.0 5.50 1.37 6.59 Dual phase change (%)−24.4 52.8 52.2 33.4 Filter media 17 Single phase 99.7 0.36 0.09 0.80Dual phase 99.2 0.55 0.13 1.15 Dual phase change (%) −.05 52.8 50.0 43.8

The optimized dual phase filter media showed from about 23% to about 52%increase in DHC and specific DHC compared to the single phase filtermedia, while strength loss in the dual phase filter media averaged about10% compared to the single phase filter media.

Other embodiments are in the claims.

1. (canceled)
 2. A filter medium, comprising: a first phase comprising afirst plurality of fibers and a second plurality of fibers differentfrom the first plurality of fibers; a second phase comprising a thirdplurality of fibers and a fourth plurality of fibers different from thethird plurality of fibers, the third plurality of fibers being the sameas or different from the first or second plurality of fibers and thefourth plurality of fibers being the same as or different from the firstor second plurality of fibers; and a transition phase between the firstand second phases, wherein the transition phase comprises at least aportion of the first plurality of fibers, at least a portion of thesecond plurality of fibers, at least a portion of the third plurality offibers, and at least a portion of the fourth plurality of fibers, andwherein at least a portion of the first plurality of fibers, at least aportion of the second plurality of fibers, at least a portion of thethird plurality of fibers, and at least a portion of the fourthplurality of fibers are intermingled with each other, wherein the airpermeability of the first plurality of fibers is higher than the airpermeability of the second plurality of fibers, the air permeability ofthe third plurality of fibers is higher than the air permeability of thefourth plurality of fibers, wherein a weight ratio of the firstplurality of fibers to the second plurality of fibers is from about50:50 to about 97:3, wherein the basis weight ratio of the first phaseto the second phase is from about 30:70 to about 70:30, wherein thefirst and second phases form a wet laid structure, wherein the first,second, third and fourth pluralities of fibers are wet laid, wherein thefilter medium has a dust holding capacity from about 1 g to about 3 gmeasured according to a Palas flat sheet test.
 3. The filter medium ofclaim 2, wherein the air permeability of the second or fourth pluralityof fibers is from about 5 CFM to about 50 CFM.
 4. The filter medium ofclaim 2, wherein the air permeability of the second plurality of fibersis from about 15 CFM to about 25 CFM.
 5. The filter medium of claim 2,wherein the air permeability of the first or third plurality of fibersis from about 50 CFM to about 350 CFM.
 6. The filter medium of claim 2,wherein the air permeability of the first or third plurality of fibersis from about 100 CFM to about 200 CFM.
 7. The filter medium of claim 2,wherein the filter medium comprises a binder.
 8. The filter medium ofclaim 7, wherein the binder is at most 35% of the basis weight of thefilter medium.
 9. The filter medium of claim 7, wherein the binder is atmost 25% of the basis weight of the filter medium.
 10. The filter mediumof claim 8, wherein the binder comprises polyvinyl acetate, an epoxy, apolyester, a polyvinyl alcohol, and/or an acrylic.
 11. The filter mediumof claim 2, wherein each of the first, second, third, and fourth fibersare formed of an organic polymeric material.
 12. The filter medium ofclaim 2, wherein the filter medium has an air permeability of about 2CFM to about 200 CFM.
 13. The filter medium of claim 2, wherein theweight ratio of first to second phase is from about 40:60 to about60:40.
 14. The filter medium of claim 2, wherein the first phasecomprises mixture of softwood fibers and hardwood fibers.
 15. The filtermedium of claim 2, wherein the first or third plurality of fibers havean average fiber length from about 1.5 mm to about 6 mm.
 16. The filtermedium of claim 2, wherein the second or fourth plurality of fibers havean average fiber length of from about 0.5 mm to about 2 mm.
 17. Thefilter medium of claim 2, wherein the first phase has a higher airpermeability than the second phase, wherein a weight ratio of the firstand second pluralities of fibers is from about 60:40 to about 90:10, anda weight ratio of the third and fourth pluralities of fibers is fromabout 10:90 to about 50:50, and wherein the air permeability of thefirst or third plurality of fibers is from 100 CFM to 200 CFM.
 18. Thefilter medium of claim 2, wherein at least two of the first, second,third and fourth pluralities of fibers are either hardwood or softwoodfibers.
 19. The filter medium of claim 2, wherein the filter mediumincludes a weight ratio of the first and second pluralities of fibers offrom about 50:50 to about 90:10, and a weight ratio of the third andfourth pluralities of fibers of from about 10:90 to about 50:50.
 20. Thefilter medium of claim 2, wherein the mean flow pore size of filtermedium is at least about 25 microns.
 21. The filter medium of claim 2,wherein the filter medium has a mean flow pore size of from about 25microns to about 125 microns.
 22. The filter medium of claim 2, whereinthe filter medium has an initial dust capture efficiency from about 80%to about 99.5%.
 23. The filter medium of claim 2, wherein the firstphase has a higher air permeability than the second phase, wherein aweight ratio of the first and second pluralities of fibers is from about60:40 to about 90:10, and a weight ratio of the third and fourthpluralities of fibers is from about 10:90 to about 50:50, wherein thefilter medium comprises a binder, and wherein the binder is at most 25%of the basis weight of the filter medium.
 24. The filter medium of claim2, wherein the first phase has a higher air permeability than the secondphase, wherein a weight ratio of the first and second pluralities offibers is from about 60:40 to about 90:10, and a weight ratio of thethird and fourth pluralities of fibers is from about 10:90 to about50:50, and wherein the mean flow pore size of filter medium is at leastabout 25 microns.